1. Field of Invention
The invention generally relates to outdoor tiles for wall, roof and floor applications. More particularly, the invention relates to connectable tile modules that include electrical components, such as electroluminescent material, photovoltaic, or thermovoltaic cells.
2. Description of the Related Art
Providing electricity through photovoltaic and thermovoltaic cells is becoming more popular as these technologies have come down in cost and reliance on other sources of electric power is increasingly disfavored for environmental and strategic reasons. However, providing a general use tile with electrical components that is easy to install and electrically connectable to other tiles without external wiring has been elusive.
The conversion of electromagnetic radiation from thermal sources to electricity is known as thermophotovoltaic (TPV) power generation. While the overall thermal-to-electric conversion (TEC) efficiency of TPV systems has typically been lower than hoped for, recent developments in materials and techniques have changed the situation dramatically. Several rare earth oxides, for example, have been shown to have altered spectral distributions in their emission spectra, leading to a more efficient TPV operation. For example, GaAs, GaSb, InGaAs are used in thermoelectric applications.
Photovoltaics refer to cells that convert sunlight directly into electrical energy. The electricity is direct current and can be used that way, converted to alternating current through the use of an inverter, or stored for later use in a battery. Conceptually, in its simplest form, a photovoltaic device is a solar-powered battery whose only consumable is light. Because sunlight is universally available, photovoltaic devices have many advantages over traditional power sources. Photovoltaic systems are modular, and so their electrical power output can be engineered for virtually any application. Moreover, incremental power additions are easily accommodated in photovoltaic systems, unlike more conventional approaches such as fossil or nuclear fuel, which require multi-megawatt plants to be economically feasible.
Although photovoltaic cells come in a variety of forms, the most common structure is a semiconductor material into which a large-area diode, or p-n junction, has been formed. In terms of basic function, electrical current is taken from the device through a contact structure on the front that allows the sunlight to enter the solar cell and a contact on the back that completes the circuit.
The original and still the most common semi-conducting material used in PV cells is single crystal silicon. Single crystal silicon cells are generally the most efficient type of PV cells, converting up to 23% of incoming solar energy into electricity. These cells are also very durable and have proven their long life in many space related applications. The main problem with single crystal silicon cells is their production costs. Growing large crystals of silicon and then cutting them into thin (0.1-0.3 mm) wafers is slow and expensive. For this reason, researchers have developed several alternatives to single crystal silicon cells, with hopes of reducing manufacturing costs.
Alternatives to single crystal silicon cells include poly-crystalline silicon cells, a variety of “thin film” PV cells, and concentrating collectors. Poly-crystalline silicon cells are less expensive to manufacture because they do not require the growth of large crystals. Unfortunately they are less efficient than single crystal cells (15-17%). “Thin films” (0.001-0.002 mm thick) of “amorphous” or uncrystallized silicon are another PV alternative. These thin films are inexpensive, and may be easily deposited on materials such as glass and metal, thus lending themselves to mass production. Amorphous silicon thin film PV cells are widely used in commercial electronics, powering watches and calculators. The problem with these cells is that they are not very efficient (12% in the lab, 7% for commercial cells), and they degrade with time, losing up to 50% of their efficiency with exposure to sunlight.
Thin film PV cells made from other materials have also been developed in an attempt to overcome the inefficiency and degradation of amorphous silicon thin films, while retaining low production costs. Gallium arsenide (GaAs), copper indium diselenide (CuInSe2), cadmium telluride (CdTe) and titanium dioxide (TiO2) have all been used as thin film PV cells, with various efficiencies and production costs. Titanium dioxide thin films, just recently developed, are very interesting because they are transparent and can be used as windows.
In terms of artistic and practical applications (e.g. improved nighttime visibility), electroluminescent materials have become popular novelties. Electroluminescent materials, such as phosphor, emit light when a current is passed through it. Commercially available phosphor-based electroluminescent materials use, for example, zinc sulphide doped with manganese (ZnS:Mn) as amber-glowing phosphor. Making different-color luminescing material for artistic effect is a matter of blending elements that will electroluminesce with red, green, blue (or a combination of these to make light of many different colors). For example, strontium sulphide doped with copper, denoted ‘SrS:Cu’ can be “tuned” by controlling the proportions of five-neighbored and six-neighbored copper by adding the elements sodium and yttrium to the material, tipping light emission toward the greens.
While electroluminescent building tiles are not known to exist in the related art, several examples of photovoltaic cells used on roof coverings are. For example, U.S. Pat. No. 4,321,416 issued to Tennant discloses a photovoltaic module in the form of a shingle having a mounting portion and flat, flexible leads extending from each module for connection to other flexible leads or to a separately wired electrical network. Furthermore, a photovoltaic shingle system is disclosed in U.S. Pat. No. 5,437,735. These shingles are made up of a strip of roofing material with photovoltaic generating devices adhered thereto. While each strip is electrically interconnected, external leads are necessary to carry electricity away from each strip. Additionally, U.S. Pat. No. 4,860,509 by Laaly et al. describes a flexible roofing membrane with photovoltaic cells incorporated therein. A final example of a solar roof assembly is found in U.S. Pat. No. 5,316,592 issued to Dinwoodie. This patent discloses a three-element assembly in which photovoltaic cells are disposed upon an insulating element that is placed upon a roof membrane. However, as with the interconnected roofing shingles above that are applied in rolls or strips, cosmetic or structural damage to one area necessitates that the entire section, rather than an individual module, be replaced.
While all of the building materials described above are suited for roof applications, none would be practical as flooring or for wall applications because of their external lead requirements, lack of rigidity, and/or unsuitable structural characteristics. Moreover, the bulkiness and expense of having separate photovoltaic regions and mounting regions can make some of these building materials economically unattractive and difficult to install. Furthermore, none of these inventions utilize a connectable rigid tile module with an electroluminescent material, a photo- and/or thermo-voltaic cell, or a combination of these, to produce electricity and/or lighting effects. Thus, there continues to be a need for a novel and improved multiuse and connectable tile modules that (1) utilize sunlight and heat to produce and store electricity and/or lighting effects, (2) are easy to install, (3) have no external wiring requirements to interconnect with each other, (4) feature decorative illumination options, and (5) are commercially feasible to produce.